The inventors herein have recognized a need for an improved diagnostic system for a DC-DC voltage converter. The diagnostic system determines if there is an over-temperature condition in the buck mode integrated circuit or an over-temperature condition in a boost mode integrated circuit in the DC-DC voltage converter. And if so, the diagnostic system induces a first bi-directional switch and a second bi-directional switch in the DC-DC voltage converter to each transition to an open operational state.